I just bought a 1988 735iL that has a weird front end problem...it has a shimmy that starts at 40 or so MPH, and becomes almost uncoltrollable at 55MPH, except under braking, which seems to tame it somewhat. I'm puzzled about what is causing it, it's not a tire problem. I had a Honda Civic 20 years ago that did something similar, it has a bad front suspension strut that was leaking. Any thoughts?